1. Field of the Invention
The present invention relates to inorganic silicate compositions useful for compression molding of dense, hard products having high degree of thermal and electrical resistance. A particular field of interest is that of molding electrical insulator products, such as switch bases, arc chutes, and similar components of electrical control or distribution apparatus.
2. Description of the Prior Art
It has long been common practice to employ asbestos based compositions for molding of products of the type just mentioned, owing to excellent thermal and electrical resistance properties of commercially available forms of asbestos. These asbestos compositions comprise one component of a multicomponent mix containing other materials, such as magnesia, to form a somewhat fibrous mix that is mixed with phosphoric acid to provide a molding composition. It is necessary that the mix have good "pot" life; that is, that it be capable of a reasonable period of storage under ambient conditions after completion of the mixing process without acquiring a set or otherwise becoming degraded before it can be put into molds and compressed. Although the molding process is referred to as "cold molding", generally low heat is supplied to the molds during the process to cure the product before demolding. Post molding cure, as by placing the molded parts in suitable ovens under controlled temperature, is commonly employed to develop the ultimate strength and hardness desired. These asbestos-based products have served quite adequately from a functional standpoint, but the presence of asbestos fiber is objectionable from an environmental standpoint.